The present invention relates to medical devices, and particularly to expandable medical devices such as cannulas, catheters, retractors, and similar devices.
Existing cannulas and/or retractors as used in endoscopic surgery today are passive devices which are fixed in length and width. They can not be varied intraoperatively in length and width to accommodate larger devices or varying size devices through the skin.
Skin and subcutaneous (subsurface) tissues are viscoelastic: they will gradually stretch without tearing. Once the tissue is slowly stretched it maintains its expanded condition for a period of time. Alternatively, the tissue can be stretched further, for example to progressively stretch out an incision. Then, after relaxation, the tissue will regain its original unstretched condition without having been damaged.
Current methods used for retracting tissue and improving visualization are mechanical separation using metal retractors during open surgery, or the direct pressure of an unconfined flow of fluid such as water or CO2 during fiberoptic surgery. A typical mechanical external fixator has pins driven through the bones and mechanically distracts the elements of the joint. Problems with the water method include fluid extravasation including into and through the tissue itself. Increased pressure and swelling result in the area, resulting in edematous or swollen tissue. Excess pressure from mechanical retractors may cause necrosis or tissue death. With these methods, it is impossible to monitor the pressure being applied to the body tissues, and tissue damage or necrosis can result.
While operating from within the body, i.e., fiber optic assisted surgery as opposed to open surgery, there is no known way to selectively move or retract tissue, either hard tissue such as bone or soft tissue, out of the way to improve visualization. No device in use adequately allows a surgeon to create an actual space or expand a potential space in the body, by separating adjacent layers of tissue. The prior art does not disclose a retractor which is powerful enough and made of a material which is strong and resilient enough to, for example, separate tissue planes from within. Such a device, especially in the field of fiber optic surgery, would allow a surgeon to visualize and operate without using the conventional bulky and awkward mechanical retractors which require large open incisions. Such a device would also permit working within the body without damaging a great deal of tissue in the path between the skin opening and the working area, by minimizing the external orifice or skin incision.
The present invention is a system of retractors and/or cannulas with which a surgeon can use to take potential spaces within the body and turn them into existing spaces safely and easily and controllably in order to safely visualize appropriate tissue and operate. The cannula and/or retractor selectively moves appropriate tissue out of the way to enable a surgeon to see and work better within the body, and selectively moves body parts such as joint parts or soft tissue planes in order to create a space between the tissues for visualization and for working.
A cannula and/or retractor of the present invention may have a fluid-operated portion such as a balloon or bladder to retract tissue, not merely to work in or dilate an existing opening as for example an angioscope does. The fluid-filled portion is flexible, and thus there are no sharp edges which might injure tissue being moved by the retractor. The soft material of the fluid-filled portion, to an extent desired, conforms to the tissue confines, and the exact pressure can be monitored so as not to damage tissue. The expanding portion is less bulky and more compact, and the pressure it applies at the tissue edges can stop bleeding of cut tissue. These are all features not possessed by a conventional mechanical retractor.
With a typical mechanical retractor, the opening in the skin and thence inwardly must be larger than the surgical area being worked upon, in order to be able to get the mechanical retractor into position. The surgeon must damage a large amount of tissue which may be healthy, in order to expose the tissue to be worked on. The cannula and/or retractor of the present invention minimizes damage to tissue in the way of the tissue the surgeon needs to expose, which was previously cut in a large open exposure. With the cannula and/or retractor of the present invention, the opening at the skin is smaller at the skin where the device is inserted, and wider at the location inside the body where the cannula and/or retractor is expanded. The cannula and/or retractor is first placed into the body in an unexpanded condition, and then, as it is expanded, pushes tissue out of the way in deeper layers of the body one can see and safely operate on affected tissue. Thus, less undesired tissue damage occurs.
The bladder is pressurized with air or with water or another fluid. The fluid used in the bladder must be safe if it accidentally escapes into the body. Thus, besides air, such other fluids as dextrose water, normal saline, CO2, and N2 are safe. The pressure in the bladder is monitored and regulated to keep the force exerted by the retractor at a safe level for tissue to prevent tissue necrosis. The retractor can exert a pressure on the tissues of as high as the mean diastolic pressure of 100 mm of mercury, or higher for shorter periods of time, while still being safely controlled. Typical inflatable devices such as angioscopes do not have anywhere near the strength, or the ability to hold enough fluid pressure, or shapes to retract tissue as described herein. As compared to prior art devices, the retractor of the present invention operates with greater pressure within the bladder, since it is made of stronger materials such as Kevlar or Mylar which may be reinforced with stainless steel, nylon, or other fiber to prevent puncturing and to provide structural shape and support as desired. Such materials are strong enough to hold the necessary fluid pressure of about several pounds or up to about 500 mg Hg or more and exert the needed force on the tissue to be moved. The choice of material is well within the ability of one familiar with such materials and accordingly will not be gone into in further detail herein. The present retractor is thus able to exert substantially more force on adjoining tissues than a prior art device. The shapes of the retractors are specific for each application, and may include separate variable chambers which are sequentially controllable, to control the direction of tissue retraction.
Surgeons operate along tissue planes. Once a surgeon finds a tissue plane, he dissects along it, starting the separation process with the knife. The cannula and/or retractor holds the tissue layers apart and helps and eases in defining and further separating the tissue layers as the surgeon operates along the tissue planes, helping to spread and define the planes. The cannula and/or retractor helps to separate the tissue layers, increasing the space for operating, and improving the surgeon""s ability to separate and visualize, leading to better and safer surgical technique.
A preferred use for the present retractor is in the field of fiber optic surgery, including endoscopy, arthroscopy, laparoscopy, etc. which require looking into and operating within a limited space with a fiber optic light and camera. The bladder expands into an area of soft tissuexe2x80x94for example the bursaxe2x80x94and pushes it out of the way. The bladder can be left in place during the operation, or it can be deflated and removed, and the arthroscope and other instruments can be put into the space created.
The bladder may be a bellows type device in which the material does not stretch but which expands when pressurized from within and which is collapsed by the use of suction. In this case, it would preferably be made of a polymer of the class including Kevlar or Mylar fabric for strength and structural integrity. The bladder may generally also be made from any very thin walled polymer.
The bladder may also be made from a biocompatible and/or biodegradable material, so that if it can not be removed from the body for some reason, or if the surgeon desires to keep the bladder in place in the body for a period of time, it will not damage the tissue and may eventually be reabsorbed into the body. Such a biodegradable bladder may be left under the skin postoperatively to stop postoperative bleeding or to keep tissue expanded. Alternatively, the bladder may be made of a stretchable material which stretches when pressurized from within, and then collapses partially of its own accord when depressurized or also with the help of suction. The retractor may be transparent for better visibility, but it need not be for some applications. Also, the retractor can be disposable. The material choice is within the skill of the art. One surface of the bladder may be made of or have thereon a reflective surface to reflect light to see around a corner.
A most typical construction for the cannula and/or retractor of the present invention is an inflatable bladder situated on the end of a shaft, which may be flexible or rigid, which is pushed through an extra opening in a scope or cannula or through a separate portal, and which expands at the end of the shaft.
The retractor can be located on a scope, either on the end thereof or movable axially through a channel along the length of the scope. The retractor can alternatively be mounted on a cannula. The retractor can be mounted on a separate shaft passing through an existing channel in a cannula; it can be inserted through a separate hole in the cannula or the scope; or it can be inserted through a separate opening in the body. The shaft with a retractor on the end can be pushed or slid through the cannula, side by side with a scope. Alternatively, the bladder can expand out of, then recess back into, a groove on a cannula or scope. The retractor can be used to create a space right by the scope, or possibly at a location spaced from the end of the scope.
The bladder itself can be round, eccentric, oval, conical, wedge-shaped, U-shaped, curved, angled, or it may be in any shape desirable to optimize the particular application. The bladder may be irregularly shaped when inflated, that is, it may expand to a greater radius in the area where it is desired to look (where greater exposure space is needed).
Vacuum can be used to deflate the bladder. The bladder may then be removed by sliding it out the portal directly.
The present invention is described herein as relating to cannulas and/or retractors. A cannula is a device for insertion into or through body tissue to provide a working passage for surgical instruments, scopes, etc., as in endoscopic or arthroscopic surgery. A catheter, on the other hand, is an artificial fluid passage primarily used for insertion through an existing body opening. The two types of devices have very different structures and structural requirements. For example, a catheter is usually flexible, very small in diameter, and not suitable for maintaining a working passage through normally closed body tissues, while a cannula is more rigid, larger in size, and designed specifically to provide a working passage for surgical instruments and scopes through normally closed body tissues. It should be understood, however, that many of the features of the present invention can with suitable modifications be applied to the catheter art. Accordingly, the present invention is not limited to cannulas per se, but may be applicable to catheters or other devices also.
The present invention defines an active cannula or sleeve which does more than merely maintain a channel or passage. It is an active device usable to enlarge a channel or passage, to position a scope or instrument, to move or locate tissue, etc. The cannula can vary in size or shape as needed, intraoperatively. Typically, with a passive (non-expandable) cannula, a surgeon must make an incision in the skin and muscle large enough to receive the largest instrument to be passed through the incision to the surgical area. Because a cannula of the present invention is expandable, the surgeon can make a small relatively small incision, stretch the tissue with the expandable cannula, contract the cannula and remove it, allowing the skin to come back to its unstretched condition. Thus, a smaller incision can be made to fit the same size instrument. This results in less trauma and scarring and an easier operation.
Further, known cannulas are generally round, while skin expands (from an incision) in an elliptical fashion, between tissue planes. Thus, the present invention provides cannulas which are or can assume such a non-circular shape, to fit into the natural opening and cause less trauma.
The devices of the present invention are usable in endoscopic procedures generally. The devices can be used to seal off a space; to expand an existing space or a potential space for working or visualization; to move tissue (for example, to stretch an incision) or to protect it. Other uses within the skill of the art but not enumerated herein are within the scope of the invention.
The cannulas of the present invention allow for the progressive stretching of an incision in skin or subsurface tissue in order to allow improved exposure, while minimizing damage to the tissue by making the actual incision as small as possible.
In the arthroscopic model, a fixed cannula is placed through the skin to the subsurface tissues into a joint. Different size working devices (shavers, burrs, scissors, punches, scope, etc.) are placed through the cannula to visualize or to work in the subsurface area at the distal end of the cannula. The cannula can be progressively expanded or stretched radially outwardly, to stretch or expand the skin and subsurface tissues. The cannula typically expands along its entire length, although it may in some cases be expandable at selected portions along its length.
The expansion can be in a circular pattern, or it can be in an oval or elliptical or other pattern to accommodate (a) the tissue planes or (b) the instruments being inserted through the cannula.
The cannula can expand inwardly to act like a valve or a seal. Or it can expand both inward and outward.
The cannula is preferably flexiblexe2x80x94that is, it is bendable about an axis extending perpendicular to the longitudinal extent of the cannula. In other words, the cannula as a long straight object is not rigid but can bend so that it is not straight. This allows the cannula to conform to the body tissues to the extent desired.
All cannula bodies can be multi-lumen for passages through which extend structure for control of bladders, tools, scope, etc.
In a first embodiment, a cannula may be of a stretchable material (such as a polymer) which is introduced into the body with a trocar. The trocar is then removed. Progressively larger dilating devices are placed inside the stretchable cannula, as needed, to progressively stretch out the skin and tissue to a larger size in order to introduce larger instruments through the cannula. Each time the cannula is enlarged, the stretched tissue remains in its stretched condition for a period of time because of its viscoelastic properties.
One way of stretching the cannula is by placing inside the stretchable cannula a bladder (round or elongated in the shape of a sausage, for example) which can be inflated to uniformly stretch the cannula and tissue. The bladder can be deflated and removed, leaving the enlarged opening.
In a second embodiment, the cannula is itself inflatable for expansion. The cannula is basically an inflatable cylinder with expansions in both the inner diameter and the outer diameter. As inflated, the device expands to a preformed shape with the inner diameter following the outer diameter and expanding outward to create a progressively larger opening. Filaments or cords can be placed between the inner and outer walls to limit their separation from each other. The inner wall can be more rigid.
In a third embodiment, the cannula includes one or more stretchable (inflatable or expandable) parts and one or more non-stretchable parts. The non-stretchable parts can be metal or plastic pieces such as curved plates, joined by the stretchable elements which extend longitudinally between them. These stretchable elements can be bladders. As larger devices are passed through the cannula, the stretchable portions expand and the plates move outwardly to stretch an appropriate opening.
In any of these cases, one can monitor and control the amount of pressure being applied to the tissue upon expansion of the cannula, so as to not exceed a certain critical pressure and damage tissue. This can be done by monitoring the actual size of expansion, the amount of air or fluid introduced to inflate the device, the fluid pressure within the device, etc.
There are numerous possibilities of a cannula-with-bladder or (catheter-with-bladder) construct.
One specific example is an arthritis irrigation system. This is a multi-lumen tube which has one lumen/portal for inflow of irrigation fluid and a second portal for suction (return). The tube is flexible and has its distal end placed in a joint to be irrigated. The tube is fixed in place by an expanding device as discussed below. Fluid flowing through the joint flushes out debris in the joint. The device can include third or additional lumens for a scope or tools to pass through. Since the tube is both flexible and fixed in place, it can remain in the patient even when the patient is ambulatory. It thus provides a permanent passage for the surgeon to access the joint.
There can be multiple bladders at a location on the cannula, independently controlled, to position the cannula. At least one bladder is preferably at the tip of the device to expand or stretch tissue or to stabilize the device.
In any of the illustrated embodiments, the bladder can be made of a different material from the cannula, as opposed to, for example, a Fogarty catheter which is made of all one material. This will allow for variations in construction, with the bladder being made of one material to better perform its functions and the cannula or other supporting member being made of another material to better perform its functions.
The expanding (inflatable) bladders of the present invention are constructed in various manners as set forth below. The bladder can stretch cannula walls. The bladder can move tissue and allow selective manipulation of tissue, even arthroscopically. The bladder also has a tamponade effect, lessening bleeding in the surrounding tissues.
The bladder also distributes the retractive force, reducing stress on delicate tissues such as nerve tissue.
There can be one or more bladders at any given location or on any given instrument. Multiple bladders can be controlled as independent structures or as one unit. Specific structure and control is based on the particular application.
The surface of the material can be pebbled or roughened or ridged, or have serrated edges, to better grip tissue and hold the retractor in position. Of course, the surface must still remain smooth enough so that the retractor is easily removable without damage to the tissue it contacts.
The bladders can expand by well in excess of 200%.
The bladder is preferably made of an elastomeric material which is strong enough to move tissue as desired. A suitable material for the expandable bladder is Silastic(copyright) elastomer, which is available from Dow Corning in medical grades. Other suitable materials are silicone, or latex, or PVC.
The bladder may be made of a non-elastomeric material which is strong enough to move tissue as desired. A suitable material is Mylar(copyright) fabric. A non-elastomeric material may have a more controllable shape because it will not stretch. A non-elastomeric material will collapse inward automatically due to the pressure of the tissue around it, whenever it is not inflated. Many of the illustrated embodiments which are discussed as being made of an elastomeric material can also be made of a non-elastomeric material.
The expandable bladder can be made of a biodegradable material. In such a case, the biodegradable portion can be made detachable from the remainder of the retractor, so that it can be detached and left in the body after surgery. This is useful, for example, to prevent adjacent tissue planes from scarring together after surgery. The biodegradable mass will in time disappear, allowing the tissues to adjoin after they are healed.
The bladder can be made of a composite materialxe2x80x94that is, a particle or fiber-reinforced material. Many suitable materials are in use in industry. Composite materials can be made stronger while still retaining flexibility and fluid-sealing capabilities. Composite materials also provide the capability to have a bladder assume a specific shape upon expansion.
The bladder can be made of a composite biodegradable material.
The bladder(s) can be made of two different materials bonded together, such as a stretchable (low-modulus) and a non-stretchable (high-modulus) material. Mylar(copyright) and Silastic(copyright) are suitable materials, or metal for a stiff material. As the inflation fluid (typically air) is introduced, it takes the path of least resistance and the non-stretchable material fills out to its expanded shape first. Then the stretchable material expands, in a manner constrained by the already-expanded non-stretchable material.
The bladder can be made of a transparent material to provide a better view of the operating area and improved visualization.
The bladder may have a dual durometer layered construction, with a thin layer for fluid retention overlying a thicker layer for shaping. Other laminated constructions are possible, also.
The external shape of the retractor when expanded, and the amount of expansion, are designed for the specific application on which that retractor is to be used. For example, if the surgeon is working against bone, he can select a retractor which is configured so that it stays flat against the bone, and expands away in the opposite direction, to push tissue away from the bone and create a working and visualization space next to the surface of the bone.
There are several ways to control shape of expansion-thick and thin areas (gaps, ridges, stiffened areas, etc.), fiber reinforcing, dual durometer construction, different materials affixed together, tethering cords, and pre-shaping.
Upon application of a given amount of force, a thinner material will stretch more than a thicker material. Thus, all other factors being equal, an inflatable device will stretch more where it is thinner, and will stretch less where it is thicker. This occurrence can be used to control the shape into which a bladder expands when it is inflated by fluid under pressure.
As a simple example, it can readily be seen that if a bladder has one half made of a very thick material and one half made of the same material but much thinner, then upon the introduction of fluid under pressure, the thin material will stretch more quickly (easily), and the bladder will expand unevenly. The thin half of the bladder will deform more under the same pressure until the force needed to stretch it further is equal to the force needed to stretch the thicker material. The half made of the thicker material will then begin to stretch, also. Thus, the thickest point on the wall will be at the crown area (farthest out).
The areas of variation in cross section can be of various shapes and directions to control the expansion rates. For example, the circumference of a bladder can be configured as an incomplete hoop. Thus, most of the circumference is of a thicker material, while selected areas are thinner. Upon the introduction of fluid under pressure, the thinner areas will expand first, with each thicker area moving outwardly as a whole.
There can be ribs around the circumference. Areas of thickness or thinness can extend longitudinally, circumferentially, radially, or in broken segments.
A second way to control the shape of expansion is the use of a fiber reinforced (composite) material. The direction of the fibers, along with their number, spacing, layering, and length, controls the rate of expansion of the matrix material. Also, areas devoid of fibers will expand faster or further than areas with more or stiffer fibers.
Specifically, the fibers resist stretching along their length. Thus, the bladder will stretch more in a direction across the fibers, or where the fibers are not present,, than in a direction along the fibers. Fibers can be placed at the edge of the bladder to maintain the shape of the bladder when inflated. Fibers can be layered, with one layer in one direction and another layer in another direction to control expansion in the other direction. Fibers can be placed in overlapping layers, to allow expansion in one plane only.
Adding fibers makes the bladder more puncture and tear resistant. Note that the bladder can, for this purpose, also be made of or include a self-sealing material.
A third way of controlling expansion shape is to pre-shape the bladder to assume a certain form when expanded. This is done in the molding process. The bladder is typically formed on a mandrel which is of a particular shape and which is sized about half way between the unexpanded and the expanded size of the bladder.
The pre-determined shape of the unexpanded bladder is basically a combination of varying wall thickness and ribbing, made on a three part mold.
In certain experimental models constructed to date, the bladder is bonded onto a nylon stalk of 7 mm O.D. The bladder is stretched from about 3 mm to about 7 mm at its smallest dimension. This pre-stretched area puts the material under tension. Any larger diameter portions are relaxed. As the bladder is expanded, the smaller diameter portion, which is already partially expanded, stretches at a limited rate. The larger diameter portion (under no load) expands at a faster rate. They balance out at a point where all the material is under basically the same load in tension. This is the point at which the shape is attained.
It should be understood that this particular example and its dimensions are not limiting, and that any diameter can be used. This is an example of a specific sized cannula for a specific application.
With a typical material (silicone), the more you stretch the material, the more force is needed to stretch it further.
The prestretching of the bladder is done so that the bladder lies flat on the cannula body. The bonding areas are such that as the expansion takes place the material expands radially outwardly as well as axially.
It can alternately be doubled up at a certain area, such as the tip of a stalk or cannula. This will allow maximum expansion at the tip.
Tethering cords can be fixed to bladder portions and extend between them to control and/or limit the expansion of the bladder. This can be done with bladders made of a composite material or including plates or other thicker areas. In a cannula construct, the tethering cords can run between the cannula body to the crown of the bladder to control and/or limit its expansion.
Plates can be added in which will limit the shape of the bladder or create an edge. For example, if a flat plate is added, the bladder can expand in a circular fashion but the flat plate will remain flat and provide a flat area on the outside of the bladder. Or the plate can be circular, or at an angle to create an edge. There can be multiple such plates added to create specific shapes. Tethering cords can be used to extend to the plate. This can be useful in the cannula construct.
The bladder can also have a bellows-type construction for increased expansion control and structural rigidity.
Suction can be used to collapse any of the devices to facilitate removal.